United States Patent 3837255

A portable guitar chording device using battery powered logic and selection circuitry is provided for producing desired chords on a conventional guitar or other stringed musical instruments. Two sets of switches, a key signature set and a chord type set operated by one hand activate the logic circuitry to cause selection of appropriate interposer selector bars by interaction of electromagnets with permanent magnets carried on the interposer. String depression plungers are mechanically moved from a position away from the strings to a position toward the strings by depression of a hinged plate member by this same hand. However only those string-fret locations in which the interposer selector means are activated by the logic circuitry cause actual depression of the strings. The second hand of the player strumming all six guitar strings then produces harmonious chords.

Starns, Robert M. (Hammond, LA)
Witt, William W. (Richmond, TX)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
International Classes:
G10D3/08; (IPC1-7): G10D3/00
Field of Search:
View Patent Images:
US Patent References:
3568560AUTO CHORD DEVICE1971-03-09Chang et al.
1687849Playing device for guitars and similar instruments1928-10-16Schmidt
1094038N/A1914-04-21Weaver et al.

Primary Examiner:
Franklin, Lawrence R.
Attorney, Agent or Firm:
Torres, And Berryhill
Parent Case Data:

This application is a continuation-in-part of application Ser. No. 300,442 filed Oct. 25, 1972 which is now abandoned.


The present invention pertains to musical instruments and more particularly to portable apparatus for automatically selecting and depressing the strings of a stringed musical instrument for playing desired chords thereon.


In the western world the seven tone diatonic musical scale is the most commonly utilized. In the diatonic scale the notes or tones are separated by whole and half steps in a specific pattern: two hole steps; a half step; three whole steps; and another half step. The strongest tone in a particular scale is the tonic tone or note, the first tone of the scale. The tonic serves as a central point for the organization of the other tones. Tonic also gives the scale its name. For example in the D major scale, D is the tonic note. Any of the twelve half steps which are included within an octave may serve as the tonic in a diatonic major scale. This means that there are 12 different diatonic major scales. The major chords in one scale may comprise the tonic, the subdominant or supertonic chords in another scale. For example, the subdominant chord in the C major scale is the F major chord. Similarly, in the key of G the G major chord is the tonic chord, the C major chord is the subdominant chord, the D major chord is the dominant chord and the A major chord is the supertonic chord. It is thus readily apparent that in any particular key or scale, that the major chords or combination of notes are necessary to play written music.

Music is harmonized in chords which comprise groups of three or more related notes sounded simultaneously. The chords and harmonics in a piece of music are usually based on the same scale. We would thus say that they are written in the same key. Therefore, the formation of chords within the diatonic scale depends upon the simultaneous sounding of three or more notes within that scale to make a harmonious sound. All major chords are ccomposed of three notes. These are; the base or root note (for example C, in the case of the C major chord); one note a major third above the root or base note; and a third note which is a perfect fifth above that root or base note. The major chords used in most popular music are; those major chords which begin on the first note (that is the tonic chord of a particular scale); those which begin on the fourth note of the scale (which are called the subdominant chord); and those which begin on the fifth note of the scale (which are called the dominant chords).

For the twelve tones of the chromatics scale twelve major chords exist. These comprise three notes played simultaneously to form a harmonious sound. Minor chords differ from major chords in that following the base or root note the second tone in the chord is a minor third higher than the base or root note and the third note is a perfect fifth above that note as in the major chords. Therefore the difference between major and minor chords is in the lowering of the third (or lowering of the second chord tone) which is the third note from the base root from a major third to a minor third. There are then, twelve possible minor chord patterns based on each of the twelve possible diatonic scale notes in the same fashion or the twelve major chord patterns. Similarly other possible chord patterns exist which would include four notes played simultaneously in the scale. These chords include those such as the diminished or lowered seventh chords which invole four notes in the scale with the seventh note being played one half step lower or flat.

A stringed musical instrument, such as the guitar is provided with a body, neck and a head portion. The body portion support a plurality of strings which are strung longitudinally along the neck portion from the body to the head where they are wound around pegs by which the tension in the strings may be adjusted to tune the strings. Longitudinally disposed on the neck adjacent to the head is normally a finger board. The finger board has a plurality of transversely extending frets between which the strings may be depressed against the finger board thereby changing their effective length for producing a particular note. The usual guitar, by tradition, contains six strings from the low to the high end. These strings are tuned as follows: E, A, D, G, B, E. To raise the pitch of any string by one half step in the diatonic scale, the string is depressed above the nut behind the first fret on the neck of the guitar. For successive raises of one-half step in pitch the strings can be depressed over successive frets up the neck of the guitar toward the body. Thus, to play a chord on the guitar, three or more of the strings may be plucked while they are open or depressed to produce the notes required in a particular chord. It is possible that relatively complicated fingering of the strings on the fingerboard may be required to produce the desired chord.

It may be necessary to pluck several selected strings while not sounding strings which are not depressed. This follows because some chords may theoretically require more than four strings to be depressed in order to achieve a harmonious sound. For example, it might be necessary to depress four strings to achieve a particular chord. If the remaining two strings are left open and all six strings are strummed then it is possible that the tones produced by the open strings would not be harmonious with the before depressed strings. In this case the strings would have to be individually plucked rather than all strummed simultaneously. This would, of course, only occur in the case of lowered seventh chords or other more complex forms than the major chords. Thus, it is possible that some chords theoretically playable on a guitar may not be practical simply because of the fingering positions or complex plucking required in order to achieve the harmonious sounds corresponding to these chords. Also, physically handicapped people may be precluded from the pleasure of playing a stringed musical instrument altogether, due to the complex fingering required. Other people may not possess the requisite nimbleness or dexterity required to play certain chords on the guitar.

Most modern music written for the guitar has the chord written in alphabetics above the notes. In the prior art, attempts have been made to provide mechanical apparatus for selecting certain combinations of notes to be played while strumming all 6 strings of a guitar. However, the prior art arrangements have suffered from the limitation of space in the sense that the mechanical linkage required is extremely complex and bulky to select the notes for a particular chord. The invention of copendingg patent application Ser. No. 300,441 is an improvement over such prior art devices. The present application covers yet another approach to this problem.

To the present, none of the prior art devices has provided a simple and economical chord selection means which may be adapted to various types of guitars. Many guitars have different string spacing, different string to fret separation, different string height and different string tensions to produce a particular note. Moreover, all the prior art apparatus developed for the purpose of enabling chords to be played on a stringed guitar have been extremely mechanically burdensome and complex. Further, such devices have not allowed the full range of all major, minor, lowered seventh and other desired chords to be played.

Accordingly, it is an object of the present invention to provide apparatus for automatically selecting and depressing the requisite strings to produce chords on any ordinary guitar.

It is another object of the present invention to provide an electronic guitar chorder which is completely portable, in the sense that it requires no AC power main connecting wires thereto.

It is a further object of the present invention to provide a guitar chorder which may be programmed to play any of the theoretical chords available on the guitar by simple strumming in spite of the fact that as many as up to all six strings of the guitar may be required to be depressed to play a particular selected chord.

A still further object of the invention is to provide a guitar chorder which is convenient and which would enable handicapped people to play chords on a conventional guitar.

The above and other objects, features and advantages of the present invention are provided by the automatic guitar chord generator of the present invention. This generator is designed as a self contained unit which fits around the neck of the guitar and depresses the necessary string combination to form chords by the use of only two sets of switches. One of the first set of twelve switches are actuated for the particular key signature of the desired chord. Also one of a second set of up to four switches are actuated to select the type chord, such as a major chord, minor chord, lowered seventh chord, etc. These switches are finger operated. After the two switches have been selected, the fingers are used to deliver the force for depressing the strings of the guitar. The guitar strings are depressed by the operation of the mechanical force applied through the switch in the second set and through a plurality of depression modules situated along the neck of the guitar and positioned between the first four frets from the head end of the neck. As there are six strings and four fret spaces, this requires twenty four such depression modules. These allow the full range of chords on the western diatonic scale to be achieved by the present invention as desired. A single depression module comprises a magnetically actuated interposer spacer member and a depressor plunger. A depression plate which is hinged to a fixed frame member and attached to the neck of the guitar actuates all twenty four of the depression plungers each time the four fingers apply mechanical pressure to depress the strings of the guitar. However, only those plungers which encounter an interposer spacer can actually depress the strings located beneath their position on the neck of the guitar. Electronic logic means actuated by the aforementioned switches are provided for magnetically actuating the interposer spacer means as desired to produce selected note combinations. The entire unit produces minimum current drain on the battery power supply as each interposer spacer is provided with a limit switch which removes the battery connection to the logic and magnet circuitry once the depression plunger has engaged the interposer spacer member.
We claim

1. A portable chord selector for a stringed musical instrument having a sounding board and a neck portion, comprising:

2. The apparatus of claim 1 wherein said string depressor means comprise spring biased plunger means situated over each string of the instrument and in the spaces between the upper five frets on the neck of the stringed instruments.

3. The apparatus of claim 2 wherein twenty four string depressor means and twenty four interposer spacer means are utilized, each one being positioned over one of the six strings of a guitar and in the keyboard spaces between the upper five frets away from the body end of the neck of the guitar, thereby allowing the selection of any theoretically possible chord on the diatonic scale on the guitar by appropriate activation of said selector means.

4. The apparatus of claim 1 wherein said interposer spacer activator means includes electrically activated means for positioning said interposer spacer means for cooperative engagement with said string depressor means according to predetermined chord relationships.

5. The apparatus of claim 4 wherein said interposer actuator means includes plural electromagnets selectively electrically activated by D. C. current supplied by logic circuitry for positioning said selector means for cooperative engagement with said string depressor means, said logic circuitry being operable to activate only those electromagnets associated with the string and fret positions usable to produce harmonious chords on the diatonic scale.

6. The apparatus of claim 5 aand further including means, in said interposer actuator means, for shutting off the flow of D. D. current to said electromagnets once cooperative engagement between said string depressor means and said interposer spacer means is achieved.

7. The apparatus of claim 5 wherein said electromagnets selectively activated by D. C. currents supplied by said logic circuitry cause movement of said interposer activator means by interaction of the magnetic field produced by the electromagnets with the magnetic field of permanent magnets mounted on said actuator means.

8. The apparatus of claim 7 wherein said electromagnets and said permanent magnets are mounted in the apparatus with like magnetic poles aligned.

9. The apparatus of claim 5 wherein said logic circuitry acts to electrically activate any of said electromagnets associated with said actuator means independently of any other actuator means according to predetermined harmonious relationships.

10. The apparatus of claim 5 wherein said logic circuitry is activated by two sets of selection switches, a key signature switch set and a chord type set, the combination of which causes the logic circuitry to select appropriate ones of said electromagnets to produce a chord of the type and key signature selected according to the diatonic scale.

11. A portable chord selector for a stringed musical instrument such as a guitar or the like, comprising:

12. A portable chord selector for a stringed musical instrument comprising:

13. The apparatus of claim 12 wherein said base plate member is provided on both its longitudinal edges with curved lip portions to provide longitudinally extensive receptacles for said first and second lever plate means which receptacles form the hinge receptacles for said lever plate means.

14. The apparatus of claim 13 wherein said interposer activator means for initiating movement of said interposer members comprises solenoid operated plunger members in one to one relationship with said interposer members and logic circuitry for supplying a D. C. current to predetermined ones of the solenoids for activating said plunger.

15. The apparatus of claim 14 and further including means for interrupting the flow of D. C. current to said solenoid means when engagement is made between said depressor bars and the selected ones of said interposer members.

16. The apparatus of claim 14 wherein said logic circuitry includes circuitry to supply D. C. current to solenoid combinations corresponding to all major, minor and seventh chords playable on said stringed instrument.

17. The apparatus of claim 12 wherein twenty-four of said string engageable interposer members are positioned one over each of six strings of said instrument in each of the spaces between the first five frets from the string tension adjusting end of the neck of said instrument.

18. The apparatus of claim 12 wherein said interposer members are constructed of a vibration absorbtive material so that when they engage said strings a vibration damping effect is produced.

19. The apparatus of claim 12 wherein said base member is fixedly attached to the neck of said stringed instrument by clamping means which is adjustable to different neck sizes.

The present invention is best understood by reference to the following detailed description thereof when taken in conjunction with the accompanying drawings in which:


FIG. 1 is a top view showing the depression modules of a first embodiment of the present invention and their situation relative to the keyboard and neck of a typical guitar;

FIG. 2 is a view along the neck of the guitar and further illustrating the depression modules of the present invention together with the depression plate and the electronic circuitry of the first embodiment of thee invention;

FIG. 3 is a more detailed view showing an individual depression module together with a depression plunger assembly of this first embodiment;

FIG. 4 shows typical logic circuitry for implementing the depression of one of the twenty-four string positions selectable by the automatic guitar chorder of the invention;

FIG. 5 is a schematic view illustrating the automatic guitar chorder of the invention attached to the neck of the guitar and being played by a musician;

FIG. 6 is a cross sectional view showing schematically a second embodiment of a guitar chorder in accordance with the invention; and

FIG. 7 is a longitudinal section showing the chorder embodiment of FIG. 6 in more detail.


Referring initially to FIG. 5, the guitar chorder of the present invention is shown attached to the neck of a guitar and being operated by a musician. It will be noted that basically the operational aspects of the chorder refer to a plurality of switches which are operable by the one hand of a guitar player which leaves the second hand of the player free for strumming the guitar strings at the location of the body of the guitar.

The automatic guitar chorder 51 is rigidly attached to the neck 52 of the guitar by conventional attaching means such as a clamp, etc. (not shown). Primarily two sets of switches are utilized to activate the chorder 51. A first set of switches operated by movable flappers 53, 54, 55 and 56 are provided for selecting major, minor or other auxiliary type of chords. A second set of switches 57, 58, etc. consisting of twelve such switches are provided foor selecting the key signature of the particular type of chord. For example, in order to play the C major chord, the player would position his thumb on the C switch button (59 of FIG. 5) while simultaneously depressing the "major" flapper 53 toward the neck of the guitar. This action sets in motion the electromechanic chord selector as will be explained.

Referring now to FIG. 1, the top view of the neck of the guitar shows 24 string depression modules positioned between the first five frets 60, 61, 62, 63 and 64 on the neck of the guitar. The depression modules are utilized to depress the six guitar strings 65, 66, 67, 68, 69, and 70 from their normal tensioned position away from the neck 52 of the guitar downwardly thereto. The depressions modules may be housed in small plastic or other suitable material boxes which are rigidly attached to the spacing plate on the guitar.

Referring now to FIG. 2 an end view along the neck of the instrument is shown. This view illustrates one cross section of the depression module. Strings 65, 66 and 67, 68, 69 and 70 are viewed longitudinally in this view. Six of the 24 depression modules 73, 74, 75, 76, 77 and 78 are positioned over the six strings respectively. The depression modules are fixedly attached to a spacing plate 79. A hinge 80 at one side of the spacing plate 79 supports a depression plate 81. The four, chord type, selector switches 53-56 of FIG. 5 are hingedly attached at 82, 83, 84 and 85 to the depression plate 81. Twenty-four depression plungers of which 6 are shown in this view (87, 88, 89, 90, 91 and 92 in FIG. 2) are also attached to the spacing plate 79. Two end plates 93 and 94 are attached to the spacing plate 79 and to the neck of the guitar in a rigid manner. At the opposite end of the end plates 94 and 95, a back plate 96 is rigidly attached. The key selector switches (as illustrated by switch 97 of FIG. 2) are attached to the back plate 96. A printed circuit board 98 containing logic circuitry associated with the invention is also attached to the back plate 96. The functioning of this circuitry will be discussed in more detail subsequently.

It will be noted by observing FIG. 2 that as the chord type selector switches are depressed toward the neck of the guitar by the playing fingers that the depression plate will commence a rotational movement about its hinge axis 80 toward the neck of the guitar. This will cause it to engage the plungers 87-92 and cause them to depress downward toward the guitar strings. When the interposer spacers which are housed interior to the depression modules 73-78 are activated appropriately, then the string combination for producing a harmonious sounding chord is selected. Thus selection of the appropriate strings for depression is reduced to selecting the appropriate interposers.

Referring now to FIG. 3, a single representative depression module which could correspond to any of the modules of FIG. 1 or FIG. 2 is illustrated in a cutaway view which illustrates also the spacer interposer housed therein. A rigid outer housing 101 of the depression modules is secured to the spacer plate 79 by a mounting screw 102. The depressor housing is also provided with a hole at the end opposite the mounting screw 102, through which the depression plunger 103 passes. Depression plunger 103 is normally urged away from the strings by biasing spring 104 which acts against the depression plunger adjust screw 105 and its associated washer 106. The lower end of the depressor plunger has affixed thereto an engagement spring 107. The engagement spring 107 is contained inside the depressor module housing 101. Pivotally mounted inside the depressor housing 101 is the interposer spacer 110 which pivots about an axis at 111. The spacer is illustrated in three separate positions which it assumes during the operative sequence which will be subsequently explained. The longitudinal end of the interposer spacer member contains a permanent magnet 112 which is permanently attached thereto and which is in an upright position situated opposite an electromagnet 113 which is permanently fixed to the depressor module housing 101. The electromagnet 113 is energized by DC current from the logic circuitry which will be described in more detail subsequently via a connecting wire 114. A limit switch 135 which contacts the interposer spacer member 110 completes the DC energizing circuit for the electromagnet 113.

In operation, if it is desired to depress the string under the location of the particular depression module illustrated, the logic circuitry would cause the DC current to flow in the electromagnet 113. Because of the polarity arrangement of the electromagnet 113 and the fixed magnet 112 which is carried on the interposer spacer member, the interposer spacer would be moved by magnetic forces from position 1 to the position 2 as illustrated. It will be noted that position 2 of the interposer spacer 110 is such that a downward motion of the depressor plunger 103 will cause the engagement spring 107 to engage the longitudinal tip (away from the axis 111) of the interposer spacer 110. Upon a downward motion of the plunger 103 which is caused by the finger pressure applied to the depression plate as previously described, continued downward motion of the depressor plunger 103 will ultimately cause the interposer spacer member 110 to assume position 3 in which the string 115 is depressed between the two frets 117 and 118 as illustrated. Thus, when the body of the guitar is strummed a note is produced by the string 115 which corresponds to the sound for a harmonious chord.

When the mechanical force supplied by the playing hand is removed from the depression plate, the biasing spring 104 urges the depressor plunger 103 upwardly again and the interposer spacer return spring 136 returns the interposer spacer member 110 from position 3 to its original position 1. As long as the interposer spacer member 110 remains in its position 1 it will not be engaged by the depressor plunger upon downward motion of the plunger. Thus only those interposer spacers whose corresponding electromagnets 113 are energized by the logic circuitry will cause string depression on downward motion of the depressor plungers.

Referring now to FIG. 4, logic circuitry associated with the selection of a particular string (i.e. string EL 1) at a particular fret is illustrated schematically. This string is depressed when a B flat major or seventh or an F major or seventh chord is sounded or, alternatively, (if a minor chord is selected) when a B flat, an F, or D minor is selected. Voltage from a battery power supply (not shown) is transmitted via the two sets of switches (i.e. the key switches and the chord switches of FIG. 4). Suppose for example it is desired to play the F major chord. The F key switch would be selcted and the major chord switch would be selected simultaneously. In this case the F voltage would be applied to the OR circuit 320 and simultaneously to the OR circuits 321 and 318. The major switch would supply a voltage level to the AND gate 322 but since the minor chord or seventh chord switches were not depressed no voltage would be supplied to the AND gates 323 or 319. Thus a signal would be produced on line 324 from AND gate 322 and this signal would be supplied to a third OR gate 325. This signal would then be amplified by an amplifier driver circuit 326 and supplied to the solenoid coil 327 which could correspond to the depressor module housed at the location EL 1 of FIG. 1. Similarly the other string positions for F major (e.e. D-3, G-2, B-1, and EH-1) would also be selected by this selection of key switches and chord switches and the depression modules situated at these locations signaled to position the interposer spacers for interception by the plunger. Thus, on the downward motion of the plungers as supplied by the hand of the player, when the six strings of the guitar were strummed by the player, a harmonious chord of F major wouuld be sounded therefrom.

The logic circuitry required for depressing the other string positions is derived from the following table of logic equations and would generally correspond to AND and OR circuitry similar to that shown in FIG. 4 based on the logic equations from the following table.


El1 = (b♭+f) major + (B♭+F+D) Minor + (A♯+F) Seventh

El2 = (b+d+g♭) major + (B+Eb+B♭) Minor + (B+D+F♯) Seventh

El3 = (c+e♭+g) major + (C+G) Minor + (C+D♯+G) Seventh

El4 = (d♭+a♭) major + (AA♭) Minor + (C♯+G♯) Seventh

A1 = (b♭+e♭+b♭) major + (E♭+G) Minor + (A♯+D♯+F♯) Seventh

A2 = (b+e+g) major + (B+E+A♭) Minor + (B+E+G) Seventh

A3 = (c+a♭) major + (A+C+F) Minor + (C+G♯) Seventh

A4 = (d♭) major + (B♭+D♭) minor + (C♯) Seventh

D1 =(b+e♭+a♭) major + (C+E♭+A♭) Minor + (B+D♯+F+G♯) Seventh

D2 = (a+c+e) major + (A+D♯+E) Minor + (D+F♯) Seventh

D3 = (d♭+f) major + (B♭+F) Minor + (C♯) Seventh

D4 = (b♭) major + (B♭) minor

G1 = (d♭+e+a♭) major + (D♭+F+A♭) Minor + (C♯+E+G♯) Seventh

G2 = (a+d+f) major + (A+D+G♭) Minor + (B+F) Seventh

G3 = (b♭+b♭) major + (B♭+E♭+G) Minor + (C+F♯) SEventh

G4 = (b) major + Minor

B1 = (c+f+a♭) major + (A+F) Minor + (C+D+F+G♯) Seventh

B2 = (a+d♭+g♭) Major + (B♭+D♭+G♭) Minor + (A+F♯) Seventh

B3 = (b♭+d) major + (B+D+G) Minor + (A♯) Seventh

B4 = (b+e♭) maor + (C+E♭) Minor

Eh1 = (b♭+d♭+f) major + (B♭+D) Minor + (C♯+F+G) Seventh

Eh2 = (b+d+g♭) major + (B+Eb+g♭) minor + (B+D+G♯) Seventh

Eh3 = (e♭+g) major + (C+E+G) Minor + (A+D♯) Seventh

Eh4 = (e+a♭) major + (F+A♭) Minor + (A♯) Seventh

The adjusting screw 105 of FIG. 3 and its associated washer 106 may be adjusted to position the depressor plunger initially at any desired height with respect to the spacing plate 79 upon which the depressor plunger is mounted. This provides for an adjustment of the depressor plungers to compensate for guitars having different spacings between the neck or keyboard portion thereof and the strings (i.e., different fret heights). Similarly, a plurality of mounting holes may be provided in the spacing plate 79 so that mounting screws 102 and depressor plungers 103 may be adjusted in position thereon to provide for different manufacturers of guitars which have different string spacings or different neck widths.

It should be noted that in the operation of the guitar chorder of the invention that an undue current strain on the battery powering the electrical components of the system is avoided by the use of the limit switch 136 which removes current from the solenoid coil upon the interposer reaching a point between position 2 and position 3 as shown in FIG. 3. This enables the entire unit to be powered by very small battery power supply such as a rechargable nickel cadmium battery pack or flashlight batteries or the like.

Similarly, once selected a particular interposer spacer bar may be held in position for repeated strummings by the mechanical pressure of the player's fingers. This further avoid the unnecessary drain of battery current if repeated playings of the same chord are desired.

Referring now to FIG. 6 another embodiment of a guitar chorder in accordance with the concepts of the present invention is shown in a cross-sectional view taken across the neck 205 of a guitar having strings 65, 66, 67, 68, 69 and 70. A curved base plate 201 is attached via screws 202 and 203 to an adjustable clamp portion 204 about the neck 205 of the guitar. Adjusting screw 207 provides a means for adjusting the clamp 204 to fit necks of various sized guitars. Each of the sides of the base plate 201 are curved upwardly as shown at 210 and 211. These longitudinally extending curved portions of the base plate 201 form a hinge on either side of the base plate which is used as a pivot point for movable depressor plate 212 and flapper plate 226 portions of the chorder.

The depressor plate 212 is hingedly attached to the base plate 201 at right end thereof as indicated at 210. The depressor plate may move about the hinge axis and the lip 225 of the curved portion of the base plate 201 serves as a stop to limit the upward movement of the depressor plate 212 at the upward position shown in phantom view by dotted lines 222. The solid line drawing of the depressor plate 212 in FIG. 6 illustrates the plate in its most downward position of movement. The upper motion limit provided by the lip stop 225 being that illustrated by the phantom view 222. A circuit board enclosure or cover 215 is fixedly attached to the depressor plate 212 by screws 213 and 214 together with other screws not shown in FIG. 6. The enclosure 215 is provided with longitudinally extending notches 218 and 219 which are sized to receive circuit board cards 216 and 217 as illustrated.

The circuit board cover 215 also provides a base for the mounting of a plurality of button type switches 220 and 221 which are used to select the chords to be provided by the chorder in a manner similar to that described with respect to the previously discussed embodiment of the invention. Twelve such button switches are mounted thereon. A battery case or container 208 sized and shaped to hold batteries or any other type of conventional D.C. power supply is attached to the base plate 201 by screws 209 as illustrated. Mounted on the end of the battery case 208 is a mode selector switch 240. This switch 240 is connected to the logic circuitry of FIG. 4 as indicated and preferably a three position rockertype switch which rests under the thumb of the player's hand. This switch 240 determines, according to the logic circuit of FIG. 4., whether major, minor or seventh chords are selected for playing by the player. Appropriate power leads (not shown) extend from the battery case 208 to the circuit boards 216 and 217 to provide electrical power for the operation of the chorder.

The left hand upwardly curved edge of the base plate 201 of FIG. 6 provides a hinge and pivot axis for a flapper plate 226. Four depressor bars 227 (only one of which is shown in FIG. 6) are attached by screws 229 to the flapper plate 226. A plurality of springs 230 (only one of which is shown in FIG. 6) urge the flapper plate 226 upwardly in a spring biased manner. Six interposer spacer members 232 are pivotally mounted over each guitar string in the guitar fret spaces on a transverse pivot bar 231 which is attached to the base plate 201 for the support thereof. There are 24 such interposer spacer members 232 positioned to correspond to the 24 guitar fret positions illustrated and nomenclatured in FIG. 1. These interposer members 232 are preferably constructed of nylon or a similar absorbent material to prevent a tinny sound from being generated when the guitar strings are strummed.

Referring now to FIG. 7 the interposer spacer members 232 and the depressor bars 227 are shown in a side cutaway view. Associated with each interposer spacer member 232 is a solenoid operated plunger 233. These plungers 233 are actuated by solenoid coils 234 associated therewith. The solenoid coils 234 are fixedly attached to the base plate 201. The plungers 233 are normally spring biased to the left against solenoid plunger stops 237. If the solenoid corresponding to a particular fret position (such as EL1 of FIG. 1) is activated, electrical current passes through the solenoid coil 234 and urges the plunger 233 forward against the interposer spacer member 232. The interposer spacer 232 is urged forward far enough to engage the shoulder of the depressor bar 227 adjacent it. Downward movement of the associated depressor bar 227 then urges the interposer spacer members 232 into contact with the guitar string and presses the string firmly against the neck 205 of the guitar.

The interposer spacer members 232 are normally held in the upright position adjacent the solenoids 234 by coil-type springs wound about the pivot shaft 231. These springs bias the interposer spacer members 232 into a withdrawn position away from the depressor bars. This spring bias also causes the unselected solenoid plungers 233 to rest against solenoid stops 237. When the push button selector switch combination 220, 221 of FIG. 6 is pushed by the player the appropriate solenoids 234 to select the string and fret positions to be depressed for a particular chord and activated and the solenoid plungers 233 corresponding to these correct string fret combinations are urged forward moving the interposer spacer members 232 associated therewith into a position where the adjacent depressor bars 227 engage them upon downward motion of the flapper plate 226. When this occurs the interposer spacer 232 corresponding to selected string and fret positions engage the string. The second hand of the guitar player strumming all of the strings then produces a melodious chord.

In operation the player selects the particular button 220, 221 combination for the chord desired and depresses this button while simultaneously gripping the outer portion of cover plate 215. This urges the depressor plate 212 into a pivotal downward motion about hinge 210 from its upward initial position 222. Simultaneously with the depression of the button switch 220, 221 the logic circuits provided on circuit boards 216 and 217 activate the solenoid coils 234 to select the appropriate string fret combination to be depressed for the chosen chord. After sufficient downward motion of the depressor plate 212 has occurred the bearing portion thereof 228 comes into contact with the flapper plate 226. The flapper plate 226 commences a pivotal downward motion about its hinge axis 211. Continued downward pressure by the fingers of the player then causes the engagement of the depressor bars 227 with the interposer spacer member 232 which have been selected by the logic circuits as being appropriate for the chord combinations selected by the player. The interposer spacer members 232 are held in the contacting position with the guitar strings as long as the player's fingers maintain sufficient tension to overcome the biasing springs 230. When the player desires to change chords, he merely releases the finger pressure exerted on the buttons 220, 221 and allows the depressor plate 212 to return to its upward position 222. The biasing springs on the interposer spacer members 232 then cause the selected interposer spacers 232 to return to their initial upright positions as shown in FIG. 7 and cause the selected solenoid plungers 233 to return to their initial position against the solenoid stops 237. Then the changing of finger positions on the buttons 221, 220 and the mechanical force exerted by the player's fingers start the downward motion of the depressor plate 212 and flapper plate 226 again and cause the depressor bars 227 to engage the interposer spacers 232 selected for the next chord by the player.

It will be observed in this embodiment of the invention that the only electrical power needed is that required to activate the solenoid coils 234 to cause a forward motion of the relatively lightweight solenoid plungers 233 which engage the interposer spacer members 232 selected for a particular chord. A limit switch arrangement (presence not shown) in FIG. 7 or 6 may be used once the flapper plate 226 has reached the position to allow engagement of depressor bar 227 and interposer spacers 232 to disconnect the electrical power supplied from the D.C. power source contained in housing 208. Thus the power source may be conserved once the appropriate interposer spacer members 232 have been selected. The main motive force for depressing the guitar strings in their appropriate positions is provided by the mechanical force supplied by the double lever system of the depressor plate 212 and flapper plate 226.

Logic circuitry similar to that shown in FIG. 4 comprises circuit components mounted on circuit boards 216 and 217 provides the selection logic for determining which of the solenoid coils 234 are provided with electrical current to activate the corresponding interposer spacer members 232. Various conventional circuit components such as integrated circuits, transistors and resistors are illustrated in FIGS. 6 and 7. It will be understood by those skilled in the art that these may comprise conventional integrated circuits of the multiple input AND and OR gates which perform the function of selecting the correct solenoid coil 234 to be activated for a particular chord in accordance with the logic chart of Table 1. This chart provides appropriate logic connections for all major, minor and seventh chords which the player may desire to play on the guitar. The AND and OR gates of the multiple input integrated circuits provide the selection logic and the transistors illustrated in FIG. 6 provide amplification in the selection of the appropriate solenoid coils for activation.

The double hinged lever arrangement shown in the embodiment of FIGS. 6 and 7 has the advantage over the embodiment shown in FIGS. 1 and 2 of not requiring as much vertical motion of the player's hand or the depressor plate and the depressor bars to cause the engagement around the appropriate interposer spacer members with the selected string fret combinations. Also the fact that selector bars are used rather than individual selector plungers as in the initially shown embodiment provides a more rigid and reliable mechanical structure.

It will be appreciated by those skilled in the art that the arrangement of switches as shown in the illustration of FIG. 5 is intended as suggestive only and not as limitative. For example, the key selector switches could be located in the position of the flaps 53, 54, 55 and 56 of FIG. 5 rather than along the top plate as illustrated. The keyboard of twelve such key selector switches could be arranged in any suitable format and used to activate the depressor plate. In such a configuration the chord type selector switches could then be mounted along the top plate, the bottom plate or any other location as desired. What is important about the location of these switches is that they be made convenient so that a person may rather rapidly select the next chord when it is desired to play a new chord. The speed of operation of the apparatus of the invention is limited only by the ability of the operator to flex his playing hand open and closed in time to select the next desired chord. This, of course, is an inherent limitation in any stringed musical instrument.

The above description may make alternative embodiments of the present invention apparent to those skilled in the art. It is therefore the aim in the appended claims to cover all such changes and modificattions as fall within the true spirit and scope of the invention.